In one prior art about the retaining joint for fixing a cable, a protection tube is a soft tube with an annular structure. A joint has a body and a lock. An O-ring is installed within the body. The lock of the joint is firstly engaged to an outer surface of the protection tube and then a distal end of the protection tube is buckled with a confining structure. Then the body of the joint is locked with the lock and the confining structure is tightly engaged so as to form an integral body. The confining structure is a hollow annular body and an end thereof is formed with a guide angle. A plurality of confining sheets are formed on an annular surface of the confining structure. An inner surface of each confining sheet is formed with a hook for being buckled to an annular recess of the protection tube. A top end of the confining structure is formed with an inclined protruding portion which is compressed by an annular surface of the body so that the protection tube, confining structure and joint are combined as an integral body.
However in practical use, only several points of the confining structure are in contact with the recess of the protection tube. Furthermore, gaps are formed between the confining sheets and the inner wall of the body for providing a deforming space to the confining sheets. The confining sheets clamp the protection tube by the elasticity itself. Thus, the protection tube is not completely clamped. Therefore, when an external force is applied to the protection tube, the confining sheets cannot clamp the protection tube completely to make the protection tube to release. Thus the cable within the protection tube cannot be protected well. Thus the prior art cannot provide complete water-proof, insect-proof and dust-proof effects to the clamped cable.